This invention relates to horizontally split casings of turbo machines each comprising an upper half casing and a lower half casing, and more particularly to a horizontally split casing, adapted to be produced by welding, for a turbo machine, such as a centrifugal compressor or a centrifugal blower of the single-shaft, multiple-stage type.
Heretofore, it has been usual practice to produce casings of centrifugal compressors of the single-shaft, multiple-stage type by casting. The casing produced by casting suffers the disadvantages that it requires a lot of labor for production and the operation is sometimes time-consuming because defective castings are produced.
To overcome these disadvantages of production of casings by casting, it has recently become popular in some applications to rely on welding in place of casting. A casing of the welded structure includes a cylindrical diaphragm support member mounted through supports on the inner side of the cylindrical casing, and outlet scrolls formed between the diaphragm support member and the casing to guide fluid discharge by impellers disposed inwardly of the diaphragm. The casing has high strength because it is a pressure resisting member, and it is a cylindrical structure of uniform diameter to improve weldability to facilitate its production. Some disadvantages are associated with the casing of the welded structure described hereinabove. They are as follows:
(a) As noted above, the casing is a cylindrical member of uniform diameter located outside the scrolls and having high strength and improved weldability so that it is easy to produce. Because of this construction, the diameter of the casing becomes too large and its weight becomes heavy. As a result, production steps including welding steps increase in number, and production costs also increase, so that the casting becomes very expensive.
(b) The increase in the weight of the casing increases the weight of compressor or the like, thereby making it necessary to increase the ability of other peripheral equipment, for example, a maintenance crane. This inevitably raises costs of basic structures.
(c) In a turbo machine, efficiency can be improved by causing a change in the area of the scrolls to take place smoothly in going toward the inlet nozzle. However, when the casing is of the welded structure, it is quite difficult to provide this construction.